1. Field of the Invention
The present invention generally relates to the generation, manipulation and detection of plasmons in semi-conductor heterostructures, and more particularly to solitons and plasmons that can be utilized as a medium for signal transport, amplification and processing at high frequencies.
2. Related Art
In the past, surface acoustic wave (SAW) technology has been used to generate surface acoustic waves in the megahertz frequency range. This technology includes a launcher comprising a plurality of inter-digitated teeth and a receiver, positioned some distance away from the launcher, which likewise contains a plurality of inter-digitated teeth. By applying a signal to the inter-digitated teeth, a compression or surface wave is launched on the material and the wave moves throughout the material. The wave is a function of the frequency of the voltage applied between the inter-digitated teeth. The voltage applied between the inter-digitated teeth launches the surface wave on the material which moves across the material and the wave travels to the receiving set of inter-digitated teeth where it develops a voltage across that set of inter-digitated teeth. When more than two sets of inter-digitated teeth are used, one can be used to excite a surface wave which travels to the second set of inter-digitated teeth which modulates the signal which modulated signal can then be received by the third set of inter-digitated teeth.
What is needed, and has not heretofore been developed, is a method and apparatus for increasing the frequency of a surface wave from the megahertz range to the terahertz range while reducing the scale of the surface wave to a single electron layer. The applications of such a device would include a source of Terahertz radiation for Terahertz frequency range spectroscopy, signal processing and sensing.
Much attention has been focused on the collective excitation spectrum of low-dimensional semiconductor systems. Interest has been driven both by the search for novel behavior from bulk semiconductor systems, and by the challenge to fabricate and probe devices based on these low-dimensional structures. Collective excitations have been studied extensively both experimentally and theoretically, using linearized hydrodynamic models and quantum many-body formulations. The results from these models yield similar behavior in the .omega.,k regime, where k&lt;k.sub.F, the Fermi wave vector. Thusfar in the literature, there has been no treatment of the non-linear behavior of these collective excitations in low-dimensional systems. Furthermore, the non-linear regime has not been experimentally accessible due to the weak coupling schemes used for excitation, including prism and grating couplers.
Previous efforts in this area are as follows:
U.S. Pat. No. 5,612,233 to Rosner, et al., discloses a method of manufacturing a single electron component in silicon MOS technique with at least two gate levels. The first gate level is made up of fine layers having dimensions &lt;100 nanometers with the surface and side walls of the gate level provided with an insulating layer. The second gate level covers the fine components of the first gate level in at least the region of the active zone. The location and dimensions of nodes or potential barriers of the single electron component are defined by the fine structures of the first gate level.
U.S. Pat. No. 5,485,018 to Ogawa, et al., discloses a logic device on the nanometer scale providing multiple logic levels made up of asymmetrically coupled quantum point contacts and a coupling region between gate electrodes. The quantum mechanical carrier wave function within the region is a spatially asymmetric wave. By changing the energy level, the conductance of the device can be switched between multiple stable conductance levels. The device can be utilized to provide a multi-level output switched in response to terahertz pulses provided by an array of optical detectors.
U.S. Pat. No. 5,291,034 to Allam et al., discloses a nonlinear optical device which employs a GaAs, AlGaAs well configuration which laterally confines a two-dimensional electron gas to produce laterally asymmetric quantum dot structures which can be controlled by bias potentials applied to alter the lateral extent of the well. This controls the assymetry of the well and affects the non-linear optical characteristic in response to incident radiation.
U.S. Pat. No. 5,239,517, to Mariani, discloses a coplanar wave guide wherein the ground planes taper directly into the outer bus bars of the SAW transducer and the center conductor of the coplanar waveguide feeds directly to the "hot" center electrode structure of the SAW transducer.
U.S. Pat. No. 5,105,232 to del Alamo, et al., discloses a quantum field effect directional coupler. The device is comprised of two quantum waveguides closely spaced apart. An adjacent gate electrode is provided over the space between the waveguides. The probability density between the wave guides is controlled by a voltage applied to the gate electrode, which controls coherent electron tunneling between wave guides. The design allows for several couplers to be connected in order to perform multi-tasking operations.
U.S. Pat. No. 5,067,788 to Jannson, et al., discloses a high speed surface plasmon wave modulator. The modulator employs a polymer glass material and super fast electro-optic controlling medium for modulating laser light at ultra high frequencies. The modulator may be configured in a planar format by complying a guided light wave with a surface plasmon wave generated at the interface of a metal electrode and an electro-optic material.
U.S. Pat. No. 4,783,427 to Reed, et al., discloses a process for the fabrication of quantum well devices, where the quantum-wells are configured as small islands of GaAs in AlGaAs matrices. The dimensions of such well devices are on the nanometer scale. These wells are fabricated by growing an n- on n+ epitaxial GaAs structure, which is then etched to an e-beam defined pattern twice, and AlGaAs is epitaxially regrown each time.
U.S. Pat. No. 4,581,621 to Reed discloses quantum-coupled devices where there are at least two closely situated well devices. The bias between the two closely situated wells can be adjusted in order to align the energy levels of the two wells so that tunneling will occur very rapidly, on the angstrom scale. Whereas conversely, when energy levels are not aligned, tunneling will be greatly reduced. The invention further provides for the output from these quantum well devices to be coupled to macroscopic contacts.
U.S. Pat. No. 4,205,329 to Dingle, et al., discloses a technique for the synthesis of single crystal super lattices of semiconductor alloys, particularly with the fabrication of periodic structures of GaAs and AlAs. The patent further describes possible uses of the invention for waveguides, heterostructure lasers and x-ray reflectors.
None of these efforts, taken either alone or in combination, teach or suggest all of the elements of the present invention, nor disclose all of the benefits thereof.